1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a lighting unit used in a liquid crystal display.
2. Description of the Related Art
Generally, a liquid crystal display used in a notebook-size computer for example includes a liquid crystal panel and a lighting unit for illuminating the panel. Conventionally with respect to the lighting unit, various efforts have been made to achieve as uniform illumination of the liquid crystal display as possible. For example, JP-A2000-200049 discloses two kinds of lighting units described below.
A first lighting unit B1, as shown in FIG. 7A of the present application, includes a light source 80 and a light guiding plate 9A. Light emitted from the light source 80 enters into the light guiding plate 9A via a first side surface 90a and travels toward a second side surface 90b. The light guiding plate 9A has a front surface formed with a plurality of slant portions 91A. The light traveling from the first side surface 90a toward the second side surface 90b is reflected by the slant portions 91A to be emitted toward a panel P via a rear surface 92 of the light guiding plate 9A.
A second lighting unit B2, as shown in FIG. 7B of the present application, includes a light source 80, a light guiding plate 9B and a reflector 89. Light emitted from the light source 80 enters into the light guiding plate 9B via the first side surface 90a to meet the second side surface 90b. The light is subsequently reflected by the reflector 89 and travels toward the first side surface 90a. Like the first lighting unit B1 described above, the light guiding plate 9B has a front surface formed with a plurality of slant portions 91B. The light, reflected by the reflector 89 and subsequently traveling toward the first side surface 90a, is reflected by the slant portions 91B to be emitted toward the panel P via the rear surface 92 of the light guiding plate 9B.
As above described, the lighting unit B1 and the lighting unit B2 are respectively provided with a plurality of highly reflective slant portions formed on the front surface of the light guiding plate. The slant portions are provided in order to illuminate the liquid crystal panel P with light emitted from the light source 80 as uniformly as possible. However, such a conventional arrangement does not always achieve sufficiently evenly distributed light.
As explained with reference to FIG. 7A, in the lighting unit B1, light traveling from the first side surface 90a toward the second side surface 90b is reflected by the slant portions 91A and subsequently emitted from the rear surface 92 of the light guiding plate 9A. With this arrangement, light tends to be emitted in large amount around the first side surface 90a facing the light source 80, whereas light tends to be emitted in small amount around the second side surface 90b positioned far from the light source 80. As a result, it is difficult to uniformly illuminate the whole surface of the panel P. Further, in the lighting unit B1, part of the light entering into the light guiding plate 9A leaks via the second side surface 90b. This also obstructs the achievement of uniform illumination of the panel P.
On the other hand, the lighting unit B2 shown in FIG. 7B is provided with the reflector 89 positioned opposite to the light source 80 across the light guide 9B. Therefore, there is no possibility of leakage of light via the second side surface 90b of the light guide. However, light output from the rear surface of the light guiding plate 9B is also different by location in the lighting unit B2. Specifically, light tends to be emitted in large amount around the second side surface 90b, whereas light tends to be emitted in small amount around the first side surface 90a. 